What year is the car / transmission? Some early stuff still had a rear pump and a spring can come apart causing the gear to shear off ( leaving you with 1st gear only ) so there is some chance it came from there and go through.

In any event, you need to find where the spring came from.

I think there are 3 screws in a clutch drum that tend to come loose and would make metal.

Flush the trans cooler and add a filter to the _outlet_ of the cooler, these have a magnet to trap steel. If there isn't enough space for a filter inline, use a 360 * loop of hose on one end.

The converter will need to be replaced / rebuilt, converters make excellent centrifugal separators so in addition to clutch material, metal will be trapped. Look at a cut open converter and you will see lots of places for junk to hide.

If you take the valve body apart, be sure to work out some sort of tray to keep the parts inline, there are usually valves that can go in both ways but will only work properly in one direction. Google " transmission valve body tray " for an example. For more popular trans, they make VB specific trays but I doubt they make one for the .3 / .4 / .5

I'm not familiar with Transmaxx , but I see they have ties to Transtar, Recon, DACCO, Axiom Automotive Technologies. These companies have all been bought / sold / changed names over the years so who knows what the parent is.